Method for producing polished-article

ABSTRACT

A grinding apparatus  10  includes a controller  11  for controlling the entire apparatus, a grinding motor  14,  a base metal  15  to be rotated by the grinding motor  14,  and a grinding wheel  16  fixed to the base metal  15.  In a grinding step, the grinding apparatus  10  is used and a surface  19  of an object to be polished  18  is ground with the grinding wheel  16  rotating at a peripheral speed of 10 m/s or less. In the grinding step, the surface  19  of the object to be polished  18  is preferably ground with the grinding wheel  16  rotating at a peripheral speed of 0.5 m/s or more. In the grinding step, a surface of alumina, sapphire, silicon carbide, or gallium nitride is ground as the object to be polished.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing a polished-article.

2. Description of the Related Art

As a grinding method for a substrate, there has hitherto been proposed a method in which a semiconductor substrate is given a desired thickness by grinding front and back surfaces of the semiconductor substrate with a surface grinding wheel including a base metal and a balance wall projecting from a surface of an outer peripheral portion of the base metal opposite from a surface from which an annular outer peripheral wall projects, in a direction opposite from the annular outer peripheral wall (see, for example, Patent Literature 1). It is described that this method can provide a surface grinding wheel in which deformation of the base metal is suppressed and grinding quality and grinding accuracy are maintained even when the surface grinding wheel is rotated at high speed.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2005-271160

SUMMARY OF INVENTION

For example, in the grinding method described in Patent Literature 1, grinding is performed for as short a time as possible with high rotation at 1500 to 10000 rpm, and smoothness is further increased by a later polishing step. In such a grinding step, strain, a damaged layer, a microcrack, or the like is caused in the surface, and the obtained substrate has a high surface roughness. It is possible to deal with this problem by removing strain, a damaged layer, a microcrack, or the like in the later polishing step. However, the polishing step takes much time, and a long processing time is required until the completion of the grinding and polishing steps.

The present invention has been made in view of these problems, and an object of the invention is to provide a method for producing a polished-article that can further improve machining quality in a grinding step. Another object of the invention is to provide a producing method for polished-article that can further shorten the processing time.

As a result of earnest study to achieve the above main objects, the present inventors found that the machining quality in the grinding step could be further improved and the total processing time in the grinding and polishing steps could be further shortened by considering the processing time in total and reviewing working in the grinding step, and achieved the present invention.

A method for producing a polished-article of the present invention is a method that produces a polished article by polishing an object to be polished, the method for producing a polished-article including a grinding step of grinding a surface of the object to be polished with a grinding wheel rotating at a peripheral speed of 10 m/s or less.

The producing method for the polished-article according to the present invention can further improve machining quality in the grinding step and can further shorten the processing time in the grinding and polishing steps. This is because, in the grinding step, the occurrence of strain, a damaged layer, a microcrack, or the like due to machining can be further suppressed by performing low-speed grinding that was not performed before. As a result, the processing time in the grinding step is lengthened, but the time required for the polishing step after the grinding step can be greatly shortened. Thus, the processing time in the grinding and polishing steps can be shortened.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart showing an example of a substrate machining process.

FIG. 2 is a schematic structural view illustrating an example of a configuration of a grinding apparatus 10 according to an embodiment.

FIG. 3 is a schematic structural view illustrating an example of a structure of a lapping device 20 according to the embodiment.

FIG. 4 is a schematic structural view illustrating an example of a structure of a CMP device 30 according to the embodiment.

FIG. 5 shows images of surfaces after grinding in Example 1 and Comparative Example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing an example of a substrate machining process according to an embodiment of the present invention. FIG. 2 is a schematic structural view illustrating an example of a configuration of a grinding apparatus 10 according to the embodiment. FIG. 3 is a schematic structural view illustrating an example of a structure of a lapping device 20 according to the embodiment. FIG. 4 is a schematic structural view illustrating an example of a structure of a CMP (chemical mechanical polishing) device 30 according to the present invention.

A method for producing a polished-article according to the embodiment includes a cutting step of obtaining a disc-shaped object to be polished by cutting a columnar ingot (Step S100), a grinding step of grinding the object to be polished obtained by cutting (Step S110), a lapping step of polishing the ground object to be polished (Step S120), a CMP step of further performing in tandem with chemical treatment (Step S130), and a cleaning step of performing surface cleaning (Step S140), and obtains a polished article subjected to polishing. Herein, the grinding step, the lapping step, and the CMP step will be described mainly. For example, the lapping step and the CMP step may be omitted, or a step other than these steps, such as a polishing step, may be added appropriately.

For example, an object to be polished 18 includes various kinds of semiconductor wafers and single crystal wafers, and contains silicon, silicon oxide, alumina, sapphire, or silicon carbide, or a compound semiconductor such as gallium nitride, gallium phosphate, gallium arsenide, indium phosphide, lithium niobate, or lithium tantalate.

(Grinding Step)

In the grinding step, an object to be polished 18 (substrate) is ground with a grinding apparatus 10 illustrated in FIG. 2. The grinding apparatus 10 includes a controller 11 for controlling the entire apparatus, a grinding motor 14, a base metal 15 to be rotated by the grinding motor 14, and a grinding wheel 16 fixed to the base metal 15. A grinding mechanism 12 of the grinding apparatus 10 is configured as a mechanism that carries out infeed machining for grinding the object to be polished 18 with the grinding wheel 16 while axially rotating the grinding wheel 16 and axially rotating the object to be polished 18 fixed to an unillustrated fixing plate. The grinding apparatus 10 is provided with the grinding motor 14 that can output sufficient torque when the grinding wheel 16 rotates in a low-speed rotation range, for example, a rotation speed range higher than or equal to 10 rpm and less than 2000 rpm. The controller 11 controls driving of the grinding motor 14 so that the grinding motor 14 rotates at a predetermined number of rotations.

In the grinding step, a surface 19 of the object to be polished 18 is ground with the grinding wheel 16 that rotates at a peripheral speed of 10 m/s or less. This can further improve machining quality in the grinding step and can further shorten the processing time in the grinding and polishing steps. In this grinding step, the surface 19 of the object to be polished 18 is preferably ground with the grinding wheel 16 that rotates at a peripheral speed of 0.5 m/s or more. This is preferable because lengthening of the time in the grinding step can be further suppressed and the processing time in the grinding and polishing steps can be further shortened. In the grinding step, for example, the number of rotations of the grinding wheel 16 is preferably 1000 rpm or less, and more preferably 800 rpm or less. The cut amount in the grinding step can be appropriately set according to the peripheral speed of the grinding wheel 16, and for example, the cut amount is preferably within the range of 0.1 to 50 μm/min, more preferably within the range of 0.5 to 40 μm/min, and further preferably within the range of 1 to 30 μm/min.

Here, the grinding step will be described. The grinding step is generally performed while the grain cut depth is smaller than a critical cut depth Dc. This critical cut depth Dc refers to the cut amount at a transition point in a deformation process from a brittle mode to a ductile mode in ductile mode machining of a hard brittle material. The grain cut depth is inversely proportional to the peripheral speed (that is, number of rotations) of the grinding wheel. To decrease the grain cut depth, it is necessary to increase the peripheral speed of the grinding wheel. However, when the peripheral speed of the grinding wheel is increased, the load on the abrasive grains decreases, and the abrasive grains become susceptible to abrasion and wear. Although abrasion and wear of the abrasive grains are so small that they cause no problem for general materials, they become heavy particularly for a high-hardness material. This sometimes deteriorates the machining quality. In the present invention, abrasion and wear of the abrasive grains are further suppressed by further decreasing the peripheral speed of the grinding wheel.

For example, the grinding wheel 16 used in the grinding step can be formed by compacting abrasive grains of oxide, carbide, nitride, and diamond. Examples of the grinding wheel 16 are a vitrified bonded wheel to be fired at high temperature by using clay, such as feldspar, as the binder, a metal bonded wheel fixed by metal, and a resin bonded wheel to be fired at low temperature by using a synthetic resin of phenol, formalin, or the like. Since the grinding wheel 16 is rotated at low peripheral speed, which was not adopted before, in the grinding apparatus 10, the hardness, porosity, and so on thereof are appropriately adjusted. For example, the grinding wheel 16 may be an electrodeposited grain wheel in which abrasive grains are fixed by a plating layer.

(Lapping Step)

In the lapping step, the object to be polished 18 is lapped with a lapping device 20 illustrated in FIG. 3. As illustrated in FIG. 3, the lapping device includes an upper surface plate 22, a rotatable lower surface plate 23 disposed opposed to the upper surface plate 22, and disc-shaped carriers 24 to be clamped between these laps. The object to be polished 18 is placed on lower surfaces of the carriers 24. The object to be polished 18 is clamped by the upper surface plate 22 and the lower surface plate 23, and is polished with abrasive grains to increase flatness.

(CMP Step)

In the CMP step, the object to be polished 18 is chemically and mechanically polished with a CMP device 30 illustrated in FIG. 4. As illustrated in FIG. 4, the CMP device 30 includes a surface plate 32, a polishing head 33, and a slurry supply device 34. A polishing pad 40 is attached to the surface plate 32. Slurry is supplied from the slurry supply device 34 onto the polishing pad 40, and the surface plate 32 rotates. Also, the polishing head 33 rotates in the same direction as the surface plate 32 while pressing the object to be polished 18 placed on the polishing pad 40 against the polishing pad 40, and thereby chemically and mechanically polishes the surface 19 of the object to be polished 18. The slurry is supplied from the slurry supply device 34 of the CMP device 30 onto a surface of the polishing pad 40. The slurry contains an abrasive material, an acid, an oxidant, a surfactant, and water. As the abrasive material, for example, colloidal silica, fumed silica, alumina, titania, zirconia, diamond, and a mixture of these materials can be used. As the oxidant, for example, peroxide and nitrate can be used. The slurry may further contain a pH adjuster. The pH adjuster appropriately uses an acid substance or a basic substance in order to adjust the pH value of the slurry to a desired value.

According to the above-described method for producing a polished-article of the embodiment, the machining quality in the grinding step can be further improved, and the processing time in the grinding and polishing steps can be further shortened. This is because the occurrence of strain, a damaged layer, and a microcrack due to machining can be further suppressed by performing lower-speed grinding, which was not performed before, in the grinding step. As a result, the processing time in the grinding step is lengthened, but the time required for the polishing step after the grinding step can be greatly shortened. Thus, the processing time in the grinding and polishing steps can be shortened.

The present invention is not limited to the above-described embodiment, and can be carried out by various modes as long as they belong to the technical scope of the invention.

EXAMPLES

Cases in which a polished article was concretely produced will be described below as examples. The present invention is not limited to the following examples, and can be carried out by various modes as long as they belong to the technical scope of the invention.

[Production of Grinding Apparatus]

Since there has been no demand for the grinding apparatus including the grinding motor 14 that rotates at low speed and the apparatus did not exist, the above-described grinding apparatus was produced. The grinding apparatus was produced by using a grinding motor that generated sufficient torque (for example 20 to 60 N·m) when a grinding wheel was rotated at a peripheral speed of 10 m/s or less and using a controller that rotated the grinding motor at the peripheral speed of 10 m/s or less.

Example 1

A single crystal wafer of high-purity alumina was prepared, and a grinding step was performed by the grinding apparatus illustrated in FIG. 2. In the grinding step, a grinding wheel having a diameter of 150 cm was used and rotated at a peripheral speed of 10 m/s (number of rotations of 1000 rpm) to grind the alumina wafer serving as an object to be polished. At this time, the cut amount was 30 μm/min. As the grinding wheel, a vitrified bonded wheel mainly composed of glass was used.

(Lapping Step)

The above-described ground wafer was subjected to lapping. Lapping was performed for three hours by using the lapping device 20 illustrated in FIG. 3 while the number of rotations of the upper surface plate was set at 60 rpm, the number of rotations of the lower surface plate was set at 60 rpm, and abrasive grains of diamond were used.

Comparative Example 1

In Comparative Example 1, an operation similar to that of Example 1 was performed except that the grinding wheel was rotated at a peripheral speed of 15 m/s (number of rotations of 1500 rpm), the cut amount was 60 μm/min, and the lapping time was nine hours.

Examples 2 and 3

In Examples 2 and 3, operations similar to that of Example 1 were performed except that an object to be polished was a sapphire wafer and a GaN wafer, respectively.

Comparative Examples 2 and 3

In Comparative Examples 2 and 3, operations similar to that of Comparative Example 1 were performed except that an object to be polished was a sapphire wafer and a GaN wafer, respectively.

(Measurement of Surface Roughness Ra)

The surface roughnesses Ra in Examples 1 to 3 and Comparative Example 1 were measured. The measurement was taken in conformity with JIS-B0601-2001.

(Result and Study)

FIG. 5 shows images of surfaces after grinding in Example 1 and Comparative Example 1. As shown in FIG. 5, the surface roughness Ra after grinding was 0.5 μm in Comparative Example 1, whereas it was 0.1 μm in Example 1. Thus, the surface roughness was improved. Further, it was found that the occurrence of strain, a damaged layer, and a microcrack due to machining was suppressed. For this reason, the total time required until the completion of the grinding and lapping steps was 9.5 hours in Comparative Example 1, whereas it was 4.0 hours in Example 1. Thus, it was revealed that the total processing time was shortened in Example 1. This is the same for Examples 2 and 3, in which the surface roughness Ra was 0.1 μm and 0.1 μm, respectively, and was improved, compared with the surface roughnesses Ra of 0.1 μm and 0.2 μm in Comparative Examples 2 and 3. Further, in Examples 2 and 3, the total processing time in the grinding step and the lapping step was four hours and seven hours, respectively. Thus, the total processing time was shortened, compared with eight hours and fifteen hours in Comparative Examples 2 and 3. In this way, the occurrence of strain, a damaged layer, and a microcrack due to machining can be further suppressed by performing lower-speed grinding, which was not performed before, in the grinding step. As a result, it is found that the processing time in the grinding step is lengthened, but the time required for the lapping step after the grinding step can be greatly shortened and the processing time in the grinding and polishing steps can be shortened.

The present application claims priority from Japanese Patent Application No. 2013-206888 filed on Oct. 2, 2013, the entire contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The polishing method for the object to be polished according to the present invention can be used to polish a surface of an object to be polished such as a semiconductor wafer. 

What is claimed is:
 1. A method for producing a polished-article that produces a polished article by polishing an object to be polished, the method for producing a polished-article comprising a grinding step of grinding a surface of the object to be polished with a grinding wheel rotating at a peripheral speed of 10 m/s or less.
 2. The method for producing a polished-article according to claim 1, wherein the surface of the object to be polished is ground with the grinding wheel rotating at a peripheral speed of 0.5 m/s or more in the grinding step.
 3. The method for producing a polished-article according to claim 1, wherein a surface of alumina, sapphire, silicon carbide, or gallium nitride is ground as the object to be polished in the grinding step.
 4. The method for producing a polished-article according to claim 1, further comprising a lapping step of polishing the object to be polished with abrasive grains after the grinding step. 